Metabolic heat production in isometric ischaemic contractions of human adductor pollicis.

The rate of intramuscular temperature rise (dT/dt) has been measured in ischaemic isometric contractions of adductor pollicis in man as an index of the rate of energy turnover. Experiments were designed so as to compare dT/dt in contractions made at a constant force but at differing intramuscular temperatures or degrees of ischaemic fatigue. In the same experiments relaxation rate was measured. As intramuscular temperature was raised from 25 to 37 degrees C, dT/dt increased with a Q10 of 1 . 8 and was closely correlated with relaxation rate. During constant force submaximal ischaemic contractions dT/dt fell, failed to recover with ischaemic rest but did so within 10 min of restoration of the circulation. During the fatiguing contraction and recovery thereafter dT/dt was linearly correlated with relaxation rate. The results show that the rate of energy turnover at a constant force is susceptible to change in association with alteration in the contractile speed of the muscle. It is suggested that relaxation rate may be used as an index of the capacity of the muscle to liberate energy.